1. Field of the Invention
The present invention concerns improved methods for detecting micro-organisms particularly yeast and bacteria in colloidal mixtures such as beer. It is also concerned with detecting micro-organisms in air and solid samples (such as food or bacterial spores) which can be placed in a liquid phase suspension or dissolved.
The production of foodstuff and beverages such as beer is accompanied by testing for the presence of certain micro-organisms in order to ensure the quality of the end-product. The brewing process may for example require in-line testing every few hours of a sample having a volume of at least 25 ml, and preferably sample volumes of for example 250 ml. Particulate matter which may include micro-organisms, namely yeast and bacteria, must then be separated from the sample and then tested to determine the presence or absence of specific micro-organisms. Devices used to achieve this include the Bibby disposable vacuum filter unit having a flat filter with an average pore diameter of 0.45 um and the Nalgene filter holders with receivers, having a flat filter with an average pore diameter of 0.45 um or 0.2 um (see for example Merck Laboratory Supplies Catalogue 1998, p. 482). Such devices allow the filtration of maximum sample volumes of only 100 ml, have a flat surface area of 50 cm2 and can take up to 30 minutes to test a sample due to their complexity of use. Once their maximum volume has been filtered, they become blocked by particulate matter such as proteins present in the sample fluid (e.g. lager, ales and other colloidal solutions) and any subsequent filtration would require pressures so high as to cause cell lysis, preventing the detection of the micro-organisms and giving false results.
2. Description of the Related Art
Prior art devices take substantially more time to separate and detect micro-organisms from a sample than is required using the devices and methods of the present invention. WO 01/11006 discloses improvements to the prior art allowing more rapid separation and detection of micro-organisms, as well as relatively simple and easy subsequent recovery of, and thus testing for, micro-organisms. The devices and methods of the present invention are distinct from those of WO 01/11006, and in particular (as detailed below) the methods involve a washing step rather than just a resuspension step.
The devices and methods of the present invention further improve upon WO 01/11006 and the other prior art by providing a yet more rapid and simple method for the separation and detection of micro-organisms from a sample.
In particular it has been found that the devices of the present invention can rapidly detect all of the bacteria in e.g. a 100 ml volume of test solution containing as few as 1-3 bacteria. Similar results can also be achieved with larger volumes e.g. 1000 ml of lager containing 1-3 bacteria.